Why did Margot say the call-up is for Mr. Frank?

Answers
1

Mrs. Frank received the call up notice addressed to Margot. She did not want to frighten them, and said it was for Mr. Frank. Margot eventually learned that it was, in fact, for her but did not tell Anne until around the time they went into hiding. Basically, nobody wanted anyone to panic so they said it was for Mr. Frank.